英语根据句子种类与用途可以分为（以下4种）
（1）陈述句：
1肯定：He is a student ; He likes watching TV
2否定:He is not a student ; He doesn't like watching TV
（2）疑问句：
1一般疑问句；Are you a teacher ? Do you like swimming ?
2 选择疑问句；Are you a teacher or a doctor ? Do you like swimming or skating ?
3 特殊疑问句；What is your favourite food? Where did you go just now ?
4 反意疑问句:He is a student , isn't he ? She works so hard , doesn't she ?
（3）祈使句：
1肯定；Close the door please
2 否定:Don't talk in class
（4）感叹句：
1WHAT 感叹；What a nice girl she is !
2 HOW 感叹:How beautifully she sings
英语根据句子结构可以分为（三种）
（1）简单句（6种）
（2）并列句（4种）
（3）复合句（14种）
在句子中起名词作用的句子叫名词从句 (Noun Clauses）
名词从句的功能相当于名词词组, 它在复合句中能担任主语、宾语、表语、同位语等，因此根据它在句中不同的语法功能，名词从句又可分别称为主语从句、宾语从句、表语从句和同位语从句
【一】主语从句 【二】表语从句 【三】宾语从句
【四】定语从句 【五】同位语从句 【六】状语从句
其中状语从句分为以下9种
（1）时间状语从句
（2）地点状语从句
（3）条件状语从句
（4）原因状语从句
（5）让步状语从句
（6）方式状语从句
（7）比较状语从句
（8）目的状语从句
（9）结果状语从句
【一】主语从句：在主句种充当主语成分的从句叫主语从句，
引导主语从句的连词有：从属连词；连接代词；连接副词
A 从属连词：that，whether。
从属连词；that，whether引导的主语从句在主语从句中不充当任何成分,只起连接词的作用，通常不可以省略。分句置于句首时，that绝对不可以省略。如果是由It作形式主语，后面that可以省略.
1,有that 引导的主语从句如下：
1. That the driver could not control hiswar was obvious.
=It was obvious（that）the driver could notcontrol his car.
2. Thatshe was chosen made us very happy.
=it made us very happy that she was chosen
3. Thathe is still alive is sheer luck.他还活着全靠运气。
=It issheer luck that she is still alive
4. Thatthe whole project is doomed to failure is quite clear
=It isquite clear that the whole project is doomed to failure.
很清楚，整个计划注定要失败。
5. Thatyou should have to leave is a pity
=It's apity that you should have to leave.
你非走不可真是件憾事。
6. That he will refuse this piece of advice isimpossible.
=It is impossible that he will refuse this piece ofadvice
7. That they should like each other is natural
=It is natural that they should like each other
8. Thathe will not come to the meeting this evening is true
=It istrue that he will not come to the meeting this evening
9. Thathe will help others is a fact
10. That theearth turns around the sun is known to all.
=It is known to all that the earth turnsaround the sun.
11. That we can win is certain
=It is certain that we can win.
12. That you have made a mistake is a fact.
=It is a fact that you have made a mistake
13. It is ordered that we should leave at once.
14. That you don’t like him is none of my business.
用it作形式主语的that-从句有以下四种不同的搭配关系：
a. It +be +形容词+ that-从句
It isnecessary that… 有必要……
It is important that… 重要的是……
It is obvious that… 很明显……
It’s certain that… 肯定…
It is possible that... 很可能……
It is unlikely that... 不可能……
It is necessary \important \natural\... that…
It is possible that she will come back tomorrow.
It is obvious that this measure is effective.
b. It +be +V ed 分词+ that-从句
It is known to all that… 从所周知……
It has been decided that… 已决定……
It is said that... 据说……
It is known to all that... 众所周知……
It is reported that... 据报道……
It is believed that...据信……;人们相信……
It is suggested that + (should）do... 建议……
It must be admitted that…必须承认……
It cannot be denied that… 不可否认……
It must be pointed out that…需指出的是……
It was reported that 20 people were killed in the accident.
It was suggested that we shouldeat more vegetable and do more exercise
c. It + be +名词+ that-从句
It is a pity/shame that... 遗憾的是……
It is a surprise that…令人惊奇的是…
It is common knowledge that… …是常识
It is common knowledge that… 是常识
It is a fact that… 事实是……
It was a pity that we lost the match.
It was a fact that he cheated in the exam.
d. It +不及物动词+ that-分句
It appears that…似乎……
It happens that…碰巧……
It occurred to me that…我突然想起……
It occurred to methat I forgot to send this letter
It happened that I came into the office at that time.
It is important(necessary / advisable /desirable / imperative / true / strange / possible ...)that ...需要注意的是,这类主语从句中,谓语动词很多为"(should)＋动词原形",即要用虚拟语气。例如:
It isnecessary that several nurses (should) stay.
几个护士留在这儿是很有必要的。
It isimperative that everyone (should) learn from practice.
每个人都应该从实践中学习。
It isreported (well-known / hoped / thought / expected / said / believed / decided /suggested / ordered ...)that ...例如:
It issaid that many people was killed in the earthquake.
据说很多人在这次地震中丧生了。
it seems(appears / doesn’t matter / makes no difference/ ...)that ...
例如:
It makes no difference whether he willattend the meeting or not.
他是否会参加会议都无关紧要。
当用it作形式主语,而将主语从句放在句尾时,主语从句中的否定词常要前移至主句中。例如:
It doesn’t seem that they are from the sameuniversity.
It doesn’t appear that we’ll have a sunnyday tomorrow.
if 不能用在主语从句中，而是用whether，如果主语从句放在句首，不能用if引导，但是如果用it 做形式主语，而把主语从句放在句末时，也可以用if引导.或把if 改为whether
If Mary really heard him is really doubtful.
正：It was doubtful if Mary really heard him.
正: Whether Mary really heard him is really doubtful.
Whether he left (or not) is unknown
Whether he will come isnot clear.
Whether it will rainor not) is not clear
Whether he’ll come here isn’t clear. 他是否会来这里还不清楚。
Whether we will go tomorrow )hasn’t beendecided yet
Whether themeeting will be put off has not been decided yet.
Whether thepoliceman will come is not certain.
Whether the 2000Olympic Games will be held in Beijingis not known yet.
Whether we’ll gocamping tomorrow depends on the weather.
whether he likesthe job is not clear.
.注意区分it 作形式主语的主语从句与强调句
强调句句型It is/was+被强调部分+that, 去掉It is/was, that，句子仍然成立。
It is natural that they should have different views. 主语从句
It is only lately that he had had afamily himself. 强调句
What was it that he wanted? I don’tknow what it was that he wanted.
It was in the hotel where he stayed that we discussed the serious problem
8.注意it 作形式主语的主语从句和as引导非限制性定语从句引导的不同
It is known to all that the earth is round.
As is known to all. the earth is round.
B连接代词who ，what ，which,whatever, whichever, whoever (Who,whom, which, what可以和ever构成合成词，和what一样引导从句，ever起到强调作用。此类主语从句不能用形式主语it引导，它们在句子中担任成分，不能省略，语序为陈述语序)
What many scientists believe is thatthe earth is round …
Who will takepart in the meeting has not been decided.
Whoever breaksthe law will be punished.
Which studentwill win is uncertain.
Whatever was saidhere must be kept secret.
这里说的话都应当保密。
Whoever makes mistakes must correctthem.
凡犯了错误的人都必须改正。
What is neededfor success) is your hard work.
Who can join inthe sport meet) is decided by the teacher
What he needs isthat book.
What he needs aresome books.
What he needs aresome books.
Who he is andwhere he is from are important.
What he saw arethe stars in the sky
What he said atthe meeting astonished everybody present
Whoever leavesthe room last ought to turn off the lights.
C连接副词when，where， how， why等。
Why they suddenlydisappeared still remains a mystery.
When they willleave is not decided.
Where she is fromis unknown.
How we will paintthe house has not been decided.
When they will arrive has been told tothe teacher
Where we will gotomorrow hasn’t been decided yet
When he will comeis not known
When he will comeis a puzzle
Where we shallspend the holiday isn’t decided.
Where he comesfrom is a mystery.
Conclusion:主语从句作主语时，谓语动词一般用单数形式
主语从句的规律
规律一、主语从句一律用陈述语序，即主语在前，谓语在后。
规律二、连词that 在从句中无实际意义，但不能省略。
规律三、whether 可以引导主语从句，放在句首，但if不能
规律四、主语从句中的连词不能重叠使用
规律五、含主语从句的主句谓语动词多用单数第三人称形式。
规律六、what 引导的主语从句，可根据表语决定主句动词的单复数形式
规律七、主语从句为了避免头重脚轻现象，用 it 做形式主语，把从句放在后面。
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追答如果还有问题，请继续追问，如果没有，请及时采纳，谢谢！
追问从句的结构都一样吗
追答所谓从句：就是 一个主句+一个或者多个从句； 从句从当主句某一个成分
如果从句从当主句时间状语：就是时间状语从句，（一个句子做时间状语）
如果从句从当主句地点状语：就是地点状语从句 （一个句子做地点状语）
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